The open water (pelagic) habitat of Santa Monica Bay sustains an abundance of life. It is affected by nutrients, sunlight, currents, fresh water, sediments, temperature fluctuations and weather. Due in part to these ever-changing factors, the Bay's 306 square miles of pelagic habitat support a great variety of organisms. The smallest include bacteria, phytoplankton and zooplankton. The largest are whales, dolphins, sharks and large fishes. In the middle of the pelagic food web are anchovies, sardines, mackerels and squid. As with all food chains, the smaller organisms tend to be food for the larger, and variation or loss of any part of the chain affects all parts.
The Bay's pelagic habitat varies on a fairly regular, seasonal basis. Two factors that probably most affect the abundance of pelagic animals are temperature and phytoplankton production.
El Niņo events can change the species composition of the plankton and may reduce productivity due to low nutrient levels. About every three to five years, Southern California's ocean environment changes dramatically as an El Niņo occurs. During an El Niņo (Spanish for the Christ child; applied in this case because the phenomenon occurs during the Christmas season), the normal water mass off the west coast is replaced with water that is warmer, saltier, and lower in nutrients than usual. These conditions extend to water depths of 330 feet and may persist for months or years.
This habitat is also affected by municipal and industrial discharges, fallout from air pollution, and urban runoff, which sometimes discharge nutrients that cause plankton blooms and subsequent loss of oxygen in the water.
Metals and organic compounds that accumulate in the microlayer that forms the Bay's surface can be toxic to fish eggs and larvae and can cause biological abnormalities. This material ultimately accumulates in the sediment, as particulates adsorb trace metals and other contaminants and carry them to the ocean floor when they sink. The sediment toxicity resulting from such accumulation is also of great concern, because chemicals such as DDT and PCBs persist in the environment for long periods of time.